1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus having a heat dissipation unit that intercepts heat generated in a fusing unit and dissipates the heat.
2. Description of the Related Art
Typically, an image forming apparatus forms an electrostatic latent image on a photosensitive medium using a laser scanning unit in response to an image signal, develops the electrostatic latent image with a predetermined color using a developing unit, and thereby forms a desired image on a sheet of paper.
A typical image forming apparatus includes a fusing unit, which fuses the image onto the sheet of the paper by applying high-temperature heat to the image formed thereon. Since the temperature of the fusing unit is high, dissipated heat is transferred to a paper exhaust unit that exhausts the sheet of paper, by convection in which the air is used as a medium, and is then transferred to an upper cover of the image forming apparatus. As a result, the upper cover becomes hot to the user's touch.
Thus, in order to solve the problem in which the upper cover gets hot, a unit that dissipates heat generated in the fusing unit outside of the image forming apparatus is needed. Accordingly, Japanese Patent Publication No. 2000-293089, the entire contents of which are incorporated by reference, published on Oct. 20, 2003, discloses an exhaust device which dissipates heat generated in a fusing unit.
FIG. 1 is a cross-sectional schematic view of a structure of an image forming apparatus using a conventional heat dissipating unit. FIG. 2 is a perspective view of a fusing unit of FIG. 1. FIG. 3 is a cross-sectional view in which the fusing unit of FIG. 2 is cut perpendicular to a fusing roller.
Referring to FIGS. 1 through 3, a paper feed cassette 16 for stacking sheets of paper 18 is installed below a main body 15 to be loaded and unloaded. A pickup roller 17, which picks up the sheets of paper 18, and a laser scanning unit 24, which forms an electrostatic latent image on a photosensitive body 22 in response to an image signal, are installed above the paper feed cassette 16. The photosensitive body 22 on which the electrostatic latent image is formed using the laser scanning unit 24 is installed on a transfer path of the sheet of paper 18 to contact the sheet of paper 18. A toner cartridge 21 for storing toner surrounds the photosensitive body 22.
A transfer roller 26 faces the photosensitive body 22 such that the sheet of paper 18 is placed between the transfer roller 26 and the photosensitive body 22, and transfers the image formed on the photosensitive body 22 onto the sheet of paper 18.
A paper feed guide 19, which guides the sheet of paper 18 picked up by the pickup roller 17 into the main body 15, is placed at one side of the paper feed cassette 16. A resist roller 20 and a pinch roller 28, which transfer the sheet of paper 18 that passes the paper feed guide 19, are installed on the transfer path of the sheet of paper 18.
A fusing roller 31 and a pressing roller 32, which fuses the image transferred onto the sheet of paper 18 when the sheet of paper 18 is placed between the fusing roller 31 and the pressing roller 32, are installed above the photosensitive body 22 and the transfer roller 26 to face each other. A pair of paper exhaust rollers 34, which exhausts the sheet of paper 18 on which the image is fused, outside of the main body 15, are installed above the transfer roller 26.
A heat dissipating unit 33, which dissipates heat generated in the fusing roller 31, is installed above the fusing roller 31, the pressing roller 32, and the paper exhaust rollers 34.
In the heat dissipating unit 33, an external cover comprising a top surface external cover 33f, a rear surface external cover 33j, and a front surface external cover 33i are combined with an internal cover. The internal cover comprises a top surface internal cover 33e, a rear surface internal cover 33h, and a front surface internal cover 33g that are formed as a single body. An air path 36 through which air enters and leaves, is placed between the external cover and the internal cover.
Ventilation holes 40 through which air enters and leaves, are formed in the rear surface external cover 33j, and an opening 38, through which heat is dissipated by a fan 39, is formed in the front surface external cover 33i. 
A ventilation hole 40 through which air enters and leaves, is formed in the rear surface external cover 33j, and an opening 38, through which heat is dissipated by a fan 39, is formed in the front surface external cover 33i. 
In the conventional heat dissipating unit 33 having the above structure, heat generated in the fusing roller 31 is accommodated in the accommodation space 35 and is conducted to the air path 36 through the internal cover. The air that enters through the ventilation holes 40 when the fan 39 operates, flows along the air path 36 together with heat conducted through the internal cover and is exhausted through the opening 38.
The air path 36 and the accommodation space 35 formed by the external cover and the internal cover should have a sufficient size and the capacity of the fan 39 should be large enough so that the conventional heat dissipating unit 33 efficiently and effectively dissipates heat generated by the fusing roller 31. If the size of the heat dissipating unit 33 is increased, however, the size of the image forming apparatus increases, and it is difficult to decrease the size of the image forming apparatus.